Gate Valves

Gate valves (also known as knife valves or slide valves) are linear motion valves in which a flat closure element slides into the flow stream to provide shut-off. Gate valves and knife valves are designed to minimize pressure drop across the valve in the fully opened position and stop the flow of fluid completely.  The direction of fluid flow does not change, and the diameter through which the process fluid passes is essentially equal to that of the pipe. Hence, they tend to have minimal pressure drop when opened fully. 

Gate valves and knife valves are advantageous in applications involving slurries, as their “gates” can cut right through the slurry.  They are also used in applications that involve viscous liquids such as heavy oils, light grease, varnish, molasses, honey, cream and other non-flammable viscous liquids.  They are available in large sizes to better handle thick flow.   However, gate valves do have low-pressure limitations, and are not optimal in applications that require cleanliness or sanitary conditions.  They are excellent for use anywhere a shutoff valve is needed. They can also be used where throttling capabilities are desired, although this is not generally recommended as erosion of the seat and disc occurs due to the vibrations of the disk in throttling applications.

Gate valves are usually divided into two types: parallel and wedge-shaped. The parallel gate valve uses a flat disc gate between two parallel seats, upstream and downstream. Knife valves are of this type, but with a sharp edge on the bottom of the gate to shear entrained solids or separate slurries. 

In the double-disk parallel-seat type, the valve is closed by lowering the disks from the valve neck to a height equal to that of the valve seats. Once so positioned, an inclined plane mounted between the two disks coverts downward stem force into axial force and presses the parallel disks firmly against the valve seats sealing the two openings. These types of valve design can accommodate asymmetric or angularly misaligned valve seats. 

Wedge-shaped gate valves and knife valves use two inclined seats and a slightly mismatched inclined gate allowing for tight shut-off. Disk flexibility is inherent to the split wedge design. This flexibility allows the split wedge to seal more easily and it reduces stickiness between the sealing surfaces in cases where the valve seats are angularly misaligned. 

• Gate Valves Option Guide
  MDC circular C-Loc® gate valves can be fitted with optional high precision, modular mechanical position indicators (MPI). This new MPI system consists of two single pole double throw micro switches...
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• Gate Valves Introduction
  In the simplest of terms, vacuum gate valves are devices that regulate the flow of gases, fluids or materials through a structure or aperture by opening, closing or obstructing a port or passageway....
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• Circular Gate Valves Specifications
  Each valve is tested using a helium mass spectrometer leak detector calibrated for a minimum sensitivity of 2x10-10 Std. Atm. cc/sec of He. Internal welds are inspected for pits, cracks, and other...
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Part Numbers for Gate Valves